Laminated glass has been used widely for windowpanes of vehicles such as automobile, aircrafts, and buildings since glass fragments are prevented from scattering and the laminated glass is thus safe even if it is broken by external impact. As the laminated glass, those obtained by inserting an interlayer film for laminated glass made of polyvinyl acetal resin such as polyvinyl butyral resin plasticized by a plasticizer between at least one pair of glass and uniting them are exemplified.
However, although being excellent in the safety, the laminated glass using such an interlayer film for laminated glass is inferior in heat-insulating property. Although infrared rays with a wavelength of 780 nm or more than that of visible light of light rays have energy as low as about 10% as compared with ultraviolet rays, the infrared rays have high thermal effects and once absorbed in a substance, the infrared rays are released as heat and generally called heat rays since they increase temperature. Accordingly, if it is made possible to shield infrared rays (heat rays) with high thermal effects of light beam entering through the windshield and side glass of an automobile, the heat-insulating property is heightened and the temperature increase in the inside of the automobile can be suppressed. Recently, the surface area for glass opening parts tends to increase and necessity to heighten the heat-insulating property for laminated glass and supply the heat ray-cutting function has been intensified.
To deal with the requirement, Patent Document 1 discloses an interlayer film for laminated glass obtained by dispersing heat-insulating particles such as indium tin oxide fine particles (hereinafter, referred to as ITO fine particles) and antimony-doped tin oxide fine particles having the heat-insulating property in polyvinyl acetal resin. The laminated glass using such an interlayer film for laminated glass is excellent in the heat-insulating property and electromagnetic wave permeability.
However, in the case heat-insulating fine particles such as the ITO fine particles and the antimony-doped tin oxide fine particles are used for a composite material with an organic material such as resin, the fine particles may possibly deteriorate an organic material such as a matrix resin owing to the photocatalytic activity, thermal activity, surface acid activity, and surface base activity of the fine particles. Further, because of the activity of the fine particle surface, deterioration of an organic material such as a matrix resin is promoted under irradiation of high energy rays such as super UV light and super Xe light to result in a problem of deterioration of visible light transmittance. That is, with respect to the interlayer film for heat-insulating laminated glass comprising heat-insulating fine particles covered with an inert substance, a matrix resin, and a liquid plasticizer, there occurs a problem that the weather resistance duration and decrease of the visible light transmittance have a proportional relation in a weather resistance test by heat, light and the like and as compared with those using an interlayer film comprising no ITO fine particles and antimony-doped tin oxide fine particles, and visible light transmittance is considerably decreased and a yellow index value, which is an indicator of yellowness, and the b* value in CIE1976 L*a*b* display system are significantly increased.
To solve the problem, Patent Document 2 discloses technique of suppressing the photocatalytic activity of metal oxide fine particles by coating the surface of the metal oxide fine particles having a photocatalytic property with a thin layer of polysiloxane.
However, with respect to the interlayer film using such heat-insulating fine particles covered with an inter substance, although the deterioration of resin in the weather resistance test and deterioration of the optical quality can be suppressed, there occurs a new problem that the visible light transmittance of the laminated glass is decreased and the haze value increases as compared with those in the case of using heat-insulating fine particles not subjected to the surface treatment.
Patent Document 1: WO 01/25162
Patent Document 2: Japanese Kokai Publication 2000-264632